Circuits for detecting when a signal has reached a predetermined threshold are well known in the art. Typically, a reference voltage is produced which is compared with the input signal by a comparator circuit. When the input signal increases to a value equal to the magnitude of the reference voltage, the output of the comparator circuit changes state.
In many applications, especially when the principal source of power is a battery, it is desirable to reduce current consumption to a minimum. A principal disadvantage of prior art threshold detector circuits is that a large amount of power is typically consumed. In addition, circuitry for producing a voltage reference which is stable over temperature, together with a separate comparator circuit, is relatively complex.
The present invention overcomes the above-noted limitations of the prior art circuits. Power consumption is very low and is almost negligible when the input signal, typically a digital signal, is in a low state. Moreover, the entire circuit may be powered by the input signal, even though such signal may be produced by a source having limited current drive capabilities, such as the output of a logic gate. In addition, many of the functions provided by a separate voltage reference and comparator can be combined so as to minimize parts count yet provide threshold voltage stability over temperature. The subject invention is further advantageous in that it can be readily implemented in integrated circuit form.
These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following Best Mode for Carrying Out the Invention together with the drawings.